German patent application 199 13 272.0, filed Mar. 24, 1999, discloses a monitoring strategy for a drive unit of a vehicle wherein a maximum rpm is pregiven which is not be exceeded when a released accelerator pedal is recognized (idle command) and the rpm of the drive unit is limited to this maximum rpm as may be required. In this way, it is ensured that a predetermined rpm limit value is not exceeded when there is a driver command for idle. The control of the drive unit is made safe by this measure when a defect is present. What is essential is the reliable recognition of the released accelerator pedal for which, as required, a change of the corresponding measurement quantity must be adapted.
The foregoing does not only apply to this so-called monitoring rpm limiter but also to other functions which are activated with the presence of a measurement quantity in a pregiven value region (for example, by the recognition of the release of the accelerator pedal or by the actuation of the accelerator pedal such as the limiting of the torque, an idle rpm control, etcetera). The above-mentioned functions (including the monitor rpm limiter) are used, depending upon configuration, individually or in any desired combination.
U.S. Pat. No. 5,875,760 discloses deriving limit values from two measurement quantities detected by two redundant measuring devices. Reaching the idle range is indicated when there is a drop below these limit values.
It is an object of the invention to provide measures with which reaching a pregiven value region of a measurement quantity is reliably detected and especially the idle region of a measurement quantity representing the driver command for controlling a drive unit.
The method of the invention is for controlling the drive unit of a vehicle and includes the steps of: detecting a first measurement quantity; detecting a second measurement quantity and the first and second measurement quantities being redundant to each other; comparing each of the measurement quantities to a threshold value; generating signals characterizing a drop below or an increase above the threshold value; and, activating or deactivating a function for controlling the drive unit when a pregiven combination of the signals is present.
With the procedure described below, a reliable recognition of reaching a pregiven value range of a measurement quantity is provided, especially reaching of the idle range of a measurement quantity representing the driver command for controlling a drive unit. This is achieved because the suitable combination of signals ensures a recognition even under unfavorable operating conditions. The signals indicate reaching the idle region and are formed in various ways. Changes in the region of the measuring device which detects the measurement quantity are also considered.
It is especially advantageous to apply the described measures in combination with an rpm limiter or torque limiter which is activated with the idle command of the driver. With the reliable and precise recognition of the idle command (or of reaching the value range representing the idle range of at least one measurement quantity for the driver command), an omission of the activation of the rpm limiter or an unwanted activation of the rpm limiter, which would negatively affect the function of the drive unit, is effectively avoided.
It is advantageous when the described procedure is utilized in combination with a solution which recognizes leaving the idle range of the measurement quantity representing the driver command when there is a pregiven limit value. Already at an earlier limit value, a slight increase of the torque of the drive unit takes place as preparation for the driving operation to follow. In this case, the described procedure guarantees that no crossovers occur between the limit and the torque control. This is so because limiting takes place only when the idle range is actually recognized and the limiting is canceled at the start of opening the throttle flap to increase torque.
With potentiometers, the measurement quantities can become incorrect because of increased contact resistance between the potentiometer track and the potentiometer wiper contact. It is especially advantageous when using potentiometers for determining the driver command (accelerator pedal position) that the detection of the idle range and therefore the activation of the limiter is ensured also in the cases where there is a rapid release of the accelerator pedal by the driver.
It is especially advantageous that continuous torque crossovers are ensured in the idle command range when activating and deactivating the limiter.
It is especially advantageous that the limiter is always activated when the accelerator pedal is actually released and when, with the activation of the rpm limiter, no torque changes of the drive unit result which are unexpected for the driver; and, that the limiter is deactivated when the driver demands an increase of the torque via the accelerator pedal. In an advantageous manner, the torque is controlled via a filter function starting from the current value of the limiter and the command for an increase by the driver is made safe by ancillary conditions.
The use of the procedure described below is advantageous in combination with other measurement quantities such as with measurement quantities, which represent the braking command of the driver, and with the aid of which measurement quantities, for example, the presence of the brake command zero is determined.